The present invention relates to an inkjet system including a printhead comprising an ink-fillable chamber operatively connected to a piezoelectric actuator and provided with a nozzle for the ejection of ink drops in response to the energization of the actuator, said actuator being connected to a measuring circuit for measuring an electric signal generated by the actuator in response to the deformation thereof. The present invention also relates to a method of making such a system and use of said system in forming an image on a receiving material.
A system of this kind is known from European Application EP 1 013 453. This system forms part of an inkjet printer with which receiving materials can be printed. The known system is of the piezo type and has a printhead with an ink chamber (also termed an “ink duct” or, briefly, a “duct”) operatively connected to a piezoelectric actuator. In one embodiment the ink chamber has a flexible wall which is deformable by energization of the actuator connected to said wall. Deformation of the wall results in an acoustic pressure wave in the chamber which, given adequate strength, will result in ejection of an ink drop from the nozzle of that chamber. The pressure wave in turn, however, results in a deformation of the wall, and this can be fed to the piezoelectric actuator. This will generate an electrical signal under the influence of its deformation.
From this application it is recognized that an analysis of this signal can provide information as to the state of the ink chamber corresponding to the particular actuator. Thus it is possible to derive from the signal whether there is an air bubble or some other disturbance in the chamber, whether the nozzle is clean, whether there are mechanical defects in the ink chamber, and so on. In principle, any disturbance of influence on the pressure wave can be traced by analysing the signal.
A disadvantage of the known method is that the signal generated by the piezoelectric actuator in response to its deformation by the pressure wave in the duct is often very complex, apart from the possible presence of random disturbances (noise). It has been found that the pressure wave in the duct is not a simple sine curve or some other simple wave configuration. This would, in fact, result in a comparably simple electrical signal. Apparently the pressure wave is not solely determined by the deformation of the actuator directly preceding the drop ejection, but there are also a number of other events which influence the pressure wave. Another consequence of this complex pressure wave is that the signal generated by the actuator as a result of this pressure wave is also very complex. Analysis of such a complex signal requires a complex, preferably digital, measuring circuit and/or relatively long processing times. This is particularly disadvantageous, especially for printers with many ink chambers in which each ink chamber of the printer is checked for disturbances after each energization. Making each chamber measurable by such a complex circuit after each energization is economically unattractive, and in addition it will often be difficult to round off an analysis within the time available until the next ink drop should be ejected from this chamber (typically 10−4 seconds). It should be clear that, particularly for applications in which high print quality is required, for example the printing of color photographs and making publicity posters, it is desirable to check each ink chamber after each energization.